This is a Maps API version of the GAsync test mapplet. It collects the information in the info window using the same code as the mapplet version:
GAsync(
map, 'getZoom', 'getSize', 'getBounds', 'getCenter',
'fromContainerPixelToLatLng', [ new GPoint(0,0) ],
marker, 'getPoint', 'getIcon',
function( zoom, size, bounds, center, topleft, point, icon ) {
// ...open the info window...
});